Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 061147 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 647 AM EST Wed Dec 6 2017 .SYNOPSIS... A cold front today will open the door to an increasingly cold and wet pattern the remainder of the week into Saturday before a drying trend begins Sunday. Frigidly cold air will close the weekend out with widespread 20s Monday morning. Another cold front next Tuesday may bring a reinforcement of cold air. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM Wednesday...Today will be nothing less than a perfect day, for those who get to stay inside. A cold front will sweep across the area this morning leaving cloudy, rainy, and increasingly cold conditions across the area. Satellite and radar imagery tells the story this morning. An area of showers ahead of a cold front is encroaching on the I-95 corridor at this hour, with the surface boundary lagging just a bit behind that. Well aloft, latest WV imagery shows a pronounced moisture tap feeding into the Carolinas which can be traced all the way back into the tropical Pacific Ocean. Also clearly evident is a deep cyclone across the southern Hudson Bay of Canada, around which a mid-level trough is digging into the eastern CONUS. These features together will create a cloud and unsettled day, with temperatures dropping through the period. Ahead of this cold front, showers will continue to advect east into a warm (the last time this word will be used for a while) and moist airmass. Latest forecast profiles suggest PWATs climbing to near 1.6 inches by daybreak, supporting the persistence of the showers ahead of the front, and have carried likely to categorical POP through late morning. Once the front pushes offshore, which is expected to occur before noon, winds will abruptly shift to the north as high pressure expands from the Midwest. While cold fronts can frequently be drying features, the main trough axis aloft remains well to our west, so moist SW flow will continue despite the surface northerly surge. This of course creates an overrunning event, and although a period of drying is progged this aftn, isentropic lift along the 300K surface begins to increase and maximize this evening and tonight. A tight moisture gradient will exist from East to West, and the coast has the best chance for increasing stratiform rain the latter half of the near term, but as isentropic lift persists overnight the entire area may again get into a steady stratiform rain. Despite the subtle drying likely this aftn, clouds will persist as moisture remains trapped beneath a near surface inversion behind the front. A few showers are possible at any time as well thanks to weak impulses rotating up from the base of the longwave trough, although QPF will be light. Still, the combination of cool north winds, clouds, and showers, will actually cause temps to drop through the aftn, so today`s highs are occurring presently, with afternoon "highs" expected to be in the 50s, low 60s far southern zones. There will be little change in the conditions tonight, and a damp, cold, and cloudy night is forecast with mins falling back to near 40. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 330 AM Wednesday...Chief caption this period, `Cold Rain`. A moisture rich, equatorial Pacific tap caught in an amplifying upper trough will overspread a cold and moist SFC-850 layer. Several waves of upper support and enhanced kinetic energy aloft will traverse early Thursday, and again on Friday, very likely enhancing rainfall rates as isentropic lift peaks. The jetlets will bring average 50 KT H7-H8 winds during these times. QPF trends have become even more impressive now, accumulating rain totals for both THU/FRI between 1-2 inches. Highs Thursday not cracking 50 in most spots, will turn colder Friday. Surface temperatures in the low to middle 30s over the interior of SE NC late Friday night, may result in a -RA/-SN mix, accumulations not expected at this time. The veering flow aloft to westerly above the cold layer should lessen isentropic omega and PCPN rates are expected to trend lighter Friday night. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 3 PM Tuesday...850mb temperatures remain below 0C on Saturday as we remain in westerly mid level flow and between the offshore front and a moisture-starved front approaching from the NW. A very impressive disturbance (100kt and 35s-1 vort at 500mb) sharpens the upper trough on Sunday, pushing even colder air into the region. Some recovery should then be slated for Monday as the eastern trough deamplifies (while still remaining huge in expanse). This may be short-lived however as energy appears to be digging into its western edge. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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As of 12Z...Just after 12Z a cold front will move through the KFLO/KLBT terminals, then the coastal terminals several hours later. Flight categories will decrease due to post frontal MVFR cigs. The chance of IFR cigs appear low attm, but probably the best time of occurrence would be an hour or two at fropa, and at KLBT early this morning. Although rain is occurring the intensity has been light thus vsbys have been VFR for the most part. This afternoon and through the overnight time height analysis and model MOS data suggest cigs becoming VFR at KFLO/KLBT. At the coastal terminals this could occur overnight, but confidence is lower. There is a high chance of precipitation continuing this TAF valid period. Extended Outlook...MVFR/IFR due to SHRA producing ceilings and visibility restrictions through Friday. MVFR conditions on Saturday and VFR conditions on Sunday.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 330 AM Wednesday...A cold front approaching from the west will cross the waters late this morning before stalling offshore. Ahead of this front, SW winds will slowly climb towards 15-20 kts before abruptly shifting to the NW this aftn and then N tonight. A brief reprieve in speeds is forecast this aftn before a surge occurs tonight, pushing wind speeds up again near 20 kts with higher gusts. Latest buoy obs show seas of 2-4 ft, and a brief uptick to 3-5 ft is possible just ahead of the FROPA. Seas will remain primarily 2-4 ft however, and that is true even post FROPA, until the northerly surge tonight drives wave heights to 4-5 ft. These gusty winds combined with the higher seas, confused spectrum, and periods of moderate rainfall will create hazardous marine conditions much of the period, and a SCEC has been hoisted for all waters beginning at midnight and persisting into Thursday. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 330 AM Wednesday...This is going to be a difficult marine period due to unrelenting north winds around 20 KT, at times gusting higher, and 4-5 foot seas offshore. Dominant wave periods every 5-6 seconds from the N-NE will result in steep waves and bumpy navigation for small craft this period, and an underlying 1-2 ft SSE swell every 8 seconds will add turmoil. Rain periodically will reduce visibility to below 2 NM. At a minimum expect `Exercise Caution` conditions, but an `Advisory` could be required for portions of this period, given the gust potential as cold air surges across the waters. LONG TERM /SATURDAY THROUGH SUNDAY/... As of 3 PM Tuesday...Additional turning to W or even WSW then slated for Saturday, the latter depending on the strength the troughiness associated with the next approaching cold front. Behind this boundary wind turns back to the NW on Sunday along with a slight increase in wind speed and possibly wave height as cold air gets re-enforced across the region. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...JDW SHORT TERM...MJC LONG TERM...MBB AVIATION...MRR

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